1. Field of the Invention
The present invention relates to an aqueous ink for a ball point pen, more specifically to a pseudo-plastic aqueous ink for a ball point pen providing the advantages of an oil base ink-filled ball point pen.
2. Description of the Prior Art
In general, what have so far been used as inks for a ball point pen are an aqueous ink of low viscosity containing water or a water soluble solvent as a solvent and having a viscosity of 10 centipoise or lower, and an oil base ink containing a lipophilic solvent such as a mineral oil, a polyhydric alcohol, a fatty acid and Cellosolve as a solvent and having a viscosity of 1000 to 20000 centipoise.
An oil base ink-filled ball point pen using an oil base ink for a ball point pen is of a structure in which the ink adhered on a ball at a pen point through an ink reservoir having a small diameter is transferred on a paper surface by rotation of the ball and only the transferred volume of the ink is fed from the ink reservoir to the ball.
An aqueous ink-filled ball point pen using an aqueous ink for a ball point pen is of a structure in which an ink is fed to a ball surface or a paper surface by means of a capillary action of a feed prepared by binding fine fibers.
While the aqueous ink for a ball point pen and the oil base ink for a ball point pen described above each have excellent advantages respectively, they have various problems.
For example, in the aqueous ink for a ball point pen, a capillary action is used as a principle of feeding the ink because of a low viscosity thereof, wherein simple contact of the point portion of the ball point pen with paper allows the capillary action to be exerted on the contact point thereof to feed the ink, and good writing can be done on a paper surface without applying so much writing pressure, so that splitting, starving and blobbing scarcely take place. On the other hand, loading the ink directly into the ink reservoir allows the ink to leak due to vibration, impact and a rise in an external temperature to make the amount of the ink fed to the ball instable. In order to prevent this, the ball point pen requires a complicated structure having a feed prepared by binding fine fibers and has a problem that it is difficult to check the remaining amount of the ink.
On the contrary, since the oil base ink for a ball point pen has a high viscosity, blobbing of the ink from the pen point can be prevented, and the ink can be loaded directly into the ink reservoir having a small diameter. As a result, a ball point pen filled with the oil base ink is characterized by that the structure of the ball point pen can be simplified and the remaining amount of the ink can be checked by using a transparent material for the ink reservoir. On the other hand, since the ink is transferred only on the paper surface contacted with the rotating ball, splitting and starving are liable to take place if the ball rotates unstably. Further, the ink is hard to penetrate into a paper surface and therefore has a problem that blobbing in which stain is caused by the untransferred ink is liable to take place.
In order to solve such problems, an aqueous ink for a ball point pen (hereinafter referred to as a pseudo-plastic aqueous ink) to which a specific viscosity characteristic is given by adding a gelling agent and a water soluble paste to a water soluble ink is provided in recent years.
In an aqueous ink-filled ball point pen using this pseudo-plastic aqueous ink, an ink viscosity is reduced when being used to write since shearing force is applied to the ink by rotation of the ball at the tip point, so that the ball point pen can write as smoothly as conventional aqueous ink-filled ball point pens and make good writing on a paper surface. Further, blobbing of the ink from the pen point can be prevented since the ink has a high viscosity when the ball point pen is not in use. The aqueous ink-filled ball point pen using this pseudo-plastic aqueous ink makes it possible to store the ink directly into the ink reservoir and simplify the structure thereof. In addition thereto, the remaining amount of the ink can be checked by using a transparent material for the ink reservoir.
Thus, the use of a pseudo-plastic aqueous ink for a ball point pen provides a writing tool having both characteristics of an aqueous ink-filled ball point pen and an oil base ink-filled ball point pen. However, an actual preparation of a pseudo-plastic aqueous ink for a ball point pen on a trial basis shows that it is very difficult to maintain the intended quality of the ball point pen without controlling the viscosity of the ink according to the tip used. For example, if the pseudo-plastic aqueous ink having a quality which is suited to a tip for a ball having a small diameter is used for a tip for a ball having a large diameter, produced are problems that a clearance between the ball and the holder changes and blobbing and splitting are caused due to a reduction in shearing force exerted to the ink in writing and that the drying property of the drawn lines is reduced because of the excess flow amount of the ink.
The present invention has been made in order to solve the problems described above, and an object thereof is to provide a pseudo-plastic aqueous ink for a ball point pen which can meet tips under any condition for ball diameters, materials, dimensions and the like and which always provides a smooth writing and a stable flow amount without causing blobbing and splitting and is high in stability on standing and a drying property of the drawn lines.